OBJECTIVE To improve the discrimination between neoplastic and functional cysts of the ovary in order to avoid superfluous surgery. METHODS Clinical examination, including ultrasound and laparoscopy, was performed on 347 women admitted to the hospital with ovarian cysts. In addition, we evaluated the contents of the cysts cytologically as well as by determining the estradiol level in the fluid via radioimmunoassay. RESULTS No single method was able to offer definitive diagnoses distinguishing between neoplastic and nonneoplastic cysts. All methods were subject to a relatively high rate of false negative findings indicating a neoplasm. To some extent, however, they were complementary. Within our three-parameter scheme, hormonal analysis yielded the best results. Cytology had drawbacks with simple serous cystomas due to the scanty and degenerated cell material. However, in proliferating cases, carcinomas and mucinous cystomas, cytology renders nearly no false negative diagnoses. CONCLUSIONS In cases of a three-parameter indication of a neoplasm, the diagnosis may be taken as definitive, and surgery should be performed. In the case of contradictory diagnoses, surgical intervention is required on a precautionary basis. In approximately 15% of cases a nonneoplastic cyst will be removed unnecessarily. In the case of a three-parameter negative indication of a neoplasm, an expectant attitude is acceptable.